Micro-truss structured material is a polymer cellular material that can be used as is, or as a template to form other materials with ordered 3D micro-truss structures, such as metals or ceramics. Micro-truss materials are useful for a number of applications such as in lightweight structural materials; energy absorbing materials; heat transfer applications; deployable structures (space structures); conformable core structures; acoustic damping; hook and loop attachments; compliant structures; optics for sub-micron waveguide formation; single body casting/net shape manufacturing; alternate shapes for waveguide members (3D honeycomb); functionally graded structures; heat exchanger/insulator structures; 3D battery/fuel cell structures; thermal switch structures; catalyst support structures; filtration/separation structures; wicking materials/moisture control structures; directional optical coupler/flexible display structures; distributed lighting structures; electrical interconnects; sensor supports with high surface areas; biological growth templates; flexible body/reactive armors; stealth coatings; high friction/high wear surfaces; waveguides for other energy sources; flame retardant foams; etc.
U.S. Pat. No. 7,382,959, which is incorporated by reference herein in its entirety, describes a method and system of creating one or more waveguides and/or patterning the waveguides to form a three-dimensional (3D) ordered polymer micro-truss structure. The system includes one or more collimated light sources, a reservoir/mold having (or containing) photo-monomer that will polymerize at a wavelength of collimated light beams provided by the light sources, and a patterning apparatus, such as a mask with multiple apertures (open areas).
After formation of the micro-truss structure according to the above-described system and method, the polymer waveguides are still somewhat soft, so there is a tendency for the micro-truss structure to sag or collapse during post-exposure processing steps. Such distortions can largely be prevented if the nodes at the bottom surface of the micro-truss structure are also attached to a solid substrate. In a refinement of the system and method, when the polymer waveguides reach the bottom of the reservoir, they are attached to a second substrate that is placed in the mold prior to filling the reservoir with photo-monomer. The excess photo-monomer is then drained from the mold and the micro-truss structure is removed, along with the attached top and bottom substrates, for cleaning and further processing. After the micro-truss structure is cleaned, a thermal post-cure process leaves the micro-truss stiff enough to be self-supporting and the substrates can be removed.
In the above-described system and method, there is a fixed, inflexible relationship between the principal elements of the fabrication process—the mask, substrate, mold and micro-truss structure. Because the micro-truss structure is inseparable from the mask and substrates until the end of processing, the mask, substrate and mold must have the same dimensions as the finished structure.
Many projected applications of the micro-truss structured material require large area sheets or panels in order to take advantage of the unique properties of the micro-truss. Examples include structural panels for aircraft and lightweight body armor. Fabricating larger-area micro-truss structures using the system and method described above requires larger masks, substrates and molds as well as collimated light sources having larger exposure areas, which are more costly and difficult to manufacture and handle. Thus, there is a need for a system and method of creating large area polymer micro-truss structures on a scale that makes the technology useful in a wide range of applications, and economically viable for commercial manufacture.